There is a relay device which relays communication information flowing through a different communication network. When the relay device relays communication information flowing through one communication network to another communication network, the communication information of the one communication network is encapsulated and transmitted to the other communication network. Here, when a failure has occurred in the one communication network, failure occurrence information is configured to be stored in the communication information flowing through the communication network. Accordingly, when the communication information including the failure occurrence information is relayed to the other communication network, the communication information is configured to be encapsulated and relayed.
However, when the failure has occurred in the one communication network, not all failure occurrence information is stored in communication information flowing through the communication network. For example, information about signal degradation may not be stored in communication information. Accordingly, even when the signal degradation information flows through another different communication network in the above-described situation, a field in which the signal degradation information is stored in communication information flowing through the other communication network is usually absent.
For example, there is no storage area for storing signal degradation information in a synchronous digital hierarchy (SDH) network. Even when the signal degradation information generated in one network is caused to be transmitted within the SDH network, the transmission is difficult. This becomes problematic when a protection path across the SDH network and another network is configured.
Technology for detecting failure occurrence in a relay device is described in Patent document 1.